Polylactic acid resin has a high melting point and is moldable in melt, and accordingly, it is expected to be a practically excellent biodegradable polymer. Furthermore, it is expected to be used in future as a widely applicable polymer made from biomaterial, and to be made into various molded articles by injection molding, extrusion molding or the like.
However, the polylactic acid resin is inferior in impact strength and brittle, and an improvement has been desired.
On the other hand, aromatic polycarbonate resin is excellent in transparency, impact resistance and mechanical properties, and has been used in various uses such as transparent products and industrial products, but it has a drawback to be inferior in flowability, and an improvement has been desired.
In the patent reference 1, it is proposed to compound polylactic acid as an improving method of the above-mentioned flowability of the aromatic polycarbonate resin. However, there have been problems that applications of the obtained product are limited due to its pearl gloss and that its productivity is inferior due to the Barus effect at melt/kneading.
In the patent reference 2, it is proposed to compound a polycarbonate to improve impact resistant property of polylactic acid resin.
In the patent reference 3, a composition excellent in foamability in which polyisocyanate compound is compounded in polylactic acid resin and polycarbonate, polystyrene, etc., is prepared.
In the patent reference 4, a medical material in which a multi-functional triazine compound is compounded to a polymer such as polylactic acid resin and polycarbonate, is proposed.
However, the compositions of the patent references 2-4 had a problem of at least one pearl gloss or surface impact, or of being difficult to improve its flame retardancy.
By the way, it is well known to melt/mix two or more kind of polymers as a polymer blend or a polymer alloy, and it is widely used as a method for improving defects of individual polymers. However, in many of cases where two or more kinds of polymers are melted/mixed, the mixture separates into respective phases due to difference of viscosity, molecular weight and molecular structure, has a coarsely dispersed structure and raises the Barus effect at melt/kneading to cause, in most cases, a difficulty to be pelletized, and an uneven mixing is exposed on surface of the obtained injection molded article, and in appearance of the molded article, a pearl gloss, a surface exfoliation or a flow mark is often brought about.
Since the polymer blend of the polylactic acid resin and the aromatic polycarbonate resin used in the present invention also has a phase separated structure separated in the respective phases, the above-mentioned Barus effect at melt/kneading or an uneven mixing by the phase separation on surface of the obtained injection molded article are observed, and therefore, it is estimated that the above-mentioned pear gloss, surface exfoliation or flow mark are brought about.
As a method of improving such a phase separation, it is proposed to compound the following compatibilizers.
In the patent reference 5, it is proposed to melt/mix a radical reaction initiator to polylactic acid resin and polycarbonate in nitrogen atmosphere, but it was still not satisfactory in improvement of impact strength (especially, surface impact).
Furthermore, since polylactic acid resin is flammable itself, it couldn't be used for parts which require a flame retardancy. On the other hand, aromatic polycarbonate resin is known as a less flammable material than polylactic acid resin. However, since its polymer blend composition with polylactic acid resin is flammable, it couldn't be used in parts which require flame retardancy.
In the above-mentioned patent reference 1 and in the patent reference 5, it is disclosed that a flame retardant can be compounded into polylactic acid resin or the like, but any detailed method for obtaining a high flame retardancy was not disclosed.                [patent reference 1] JP Patent No. 3279768 (pages 1-2), (paragraph number [0008])        [patent reference 2] U.S. Pat. No. 5,952,450        [patent reference 3] JP-A-2000-17038 (pages 1-2)        [patent reference 4] U.S. Pat. No. 6,897,245        [patent reference 5] JP-A-2002-371172 (pages 1-2)        